1. Field of the Invention
The present invention relates to a cement admixture and a cement composition used in the civil engineering and construction fields.
2. Description of the Prior Art
There have so far been expanding agents used for the purposes of increasing the initial strength of cement concrete, preventing its cracking and introducing chemical prestress in it (Patent Publications 1-4).
In the meantime, it has been known that tin sulfates provide an effective material capable of reducing hexavalent chromium dissolving out from cement concrete (Patent Publication 5, and Non-Patent Publications 1 and 2).
Patent Publication 5 teaches to the effect that “known additives such as hardening accelerators, hardening retarders, contraction or shrinkage reducers and rebar rust-preventives and special admixtures such as expanding materials may be added, and their addition does not arise any specific problems”, but it says nothing about reductions of hexavalent chromium by combined use of tin sulfates and an expanding material.